Why does the complete wall fall over?
In this blend, you need to adjust the following to get the desired effect:

1) set Rigidbody shape to Convex Hull, this is faster and with regular voronoi geometry, more stable as well. Means the wall will not explode with lower constraints settings.

2) reduce the constraint search radius to about 5.0 and the amount of constraints to 50. Those settings apply to each mesh island, means each island searches for max. 50 neighbors in a radius of 5.0 around its centroid then.
Rule of thumb: the smaller the shards are, the smaller the search radius can become to find enough neighbors. 
You dont need 2000 constraints per Island and such a large search radius here. (btw, I work without units mostly, but this is personal preference.)

3) optionally you could make the wall animated and triggered, and the wrecking ball a trigger. With this setting the shard simulation starts only for those shards being hit by a trigger, basically. The others remain inactive, which is faster too.